The elegant-sounding fallopia japonica is described by the Environment Agency as "indisputably the UK's most aggressive, destructive and invasive plant". It is a criminal offence to plant the weed or otherwise cause it to grow in the wild. Even allowing it to encroach onto one's property from a neighbour's land can constitute a private nuisance under common law. Lenders frequently refuse mortgages on properties exposed to the knotweed.

Why the fuss? The bamboo-like weed can grow to 3-4m in just 10 weeks – the equivalent of two grown adults – while its roots, or rhizomes, can spread 7m horizontally and compromise the structure of buildings. Difficult to remove, the weed requires expert clearing which can cost homeowners in the region of £20 000 - or risk their property becoming unsaleable. The government estimates it could cost £1.5bn to clear the infestation, more than half the budget of the Department of Environment, Food and Rural Affairs.

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The weed was not always regarded as a blight on one's property. It was introduced to Britain from Japan in the 1800s by Victorian 'wild gardeners' attracted by its ornamental structure of large oval leaves and masses of creamy, heart-shaped flowers.

The Killer Shrimp

A crustacean native to the river basins of the Black and Caspian Seas, the dikerogammarus villosus was first spotted in the UK near Cambridge in 2010. Measuring between 3mm and 30mm, the shrimp is smaller than your usual moster of the deep, but it has been preying on British invertebrates such as native shrimp and smaller fish - hence the moniker 'killer shrimp' or 'demon shrimp'.

The Eastern European critters freqently hitchhike in the kit of fishermen and canoeists and spread to other areas by their ability survive out of the water for up to two weeks.

The killer shrimp is on an EU blacklist of species that are of "Union Concern".

The North American Signal Crayfish

A North American signal crayfish (PA)

Pacifastacus ieniusculus, or the signal crayfish, introduced from across the pond in the 1970s to be farmed, has since escaped to a variety of locations across the UK.

They carry a disease, the crayfish plague, which is fatal for Britain's native white-claw crayfish, an endangered species, while not affecting themselves. Bigger and more aggressive than other crayfish, signal crayfish out-compete native species for nutrition and habitation.

The Grey Squirrel

A Grey Squirrel (PA)

The eastern grey squirrel was first brought to Britain from the United States as a fashionable addition to estates. However, the sciurus carolinensis was later found to be carrying the squirrel pox, to which native red squirrels are not immune.

The red squirrel population has declined dramatically in England, where it is estimated that only 30 000 remain, although populations continue to thrive in the north-east.